"Now, don't be tempted to go off and have a romantic moment in the bushes. There are a lot of cockroaches, and they will win." An usher is delivering this rather unusual pre-show admonition to a slightly chilly huddle of night-time visitors to Edinburgh's Royal Botanic Garden. The show in question is called Power Plant – a series of spectacular sound and light installations animating the garden's beautiful glasshouses.

The nocturnal gardens – quiet, moonlit and deeply shadowed – are a world away from their cheerful daytime incarnation. The palm house's facade is lit up in a series of bold striations that seem to transform its elegant architecture into something alien, even sinister.

Inside, the space is illuminated briefly, and an odd, deep, husky sound is heard, as if produced by long-disused organ pipes. For one unnerving moment it seems as if the palms themselves have broken into some strange primeval song.

Things are about to become even stranger. It turns out that the organ whistles are powered by vacuum cleaners – inspired when artist Mark Anderson "kept seeing vacuum cleaners in skips in Wales, and I thought, what a waste". The work is called Lupus sonitus – all the installations in the show are given faux-botanical names and are identified by plant labels.

Next up, is a whirling second world war siren, "which a friend found on a scrapheap and I inherited," says Anderson. "After that I started collecting sirens." Lamentor carmen (common name, siren song), is a choir of 23 of them, haunting and melancholy. "Of course I can't practise with them at home," he says. "The neighbours don't really like it."

Things turn nasty in the hot, damp cycad house. In the gloom it is hard to pick out what's going on, and there is some terrifying foliage dangling from above that brushes your face like lank hair. Something at the heart of the space appears to be breathing, and as it breathes it becomes illuminated. It is a pulsing, swelling presence that almost looms from unwholesomely orchid-scented hothouse. "I want danger and beauty to lurk there," says Anderson. "These are psycho-cycads."

In one conservatory, old-fashioned gramophones are playing, not records, but discs cut from artificial turf, while a disco ball hung from the branches of a tree scatters droplets of light. "I started making 7in discs from all kinds of different materials," says Kirsten Reynolds. "Someone said to me: 'They look very pretty, but it's a shame you can't play them.' I don't like being told what to do so I started to experiment. You can pass a needle over a surface and it becomes an instrument. It creates a loop that slightly fluctuates, and has a natural rhythm to it." Other discs are made from wood or from circular saws. When Power Plant was originally made, in the botanical gardens in Oxford, she used thorns from a tree as her stylus.

Visitors wend their way outside to be greeted by blasts of flame accompanied by deep, breathy, husky notes, as if a group of dragons were attempting a singsong. These are the Pyrophones, by Anderson and Nick Sales. Two men lurk at a desk, controlling the choreography of the fire. Though the human agency in Power Plant can often only be glimpsed, this is a live performance. "People tend to assume that the whole thing is automated," says Reynolds. "That's not the case at all. There are a few boxes with knobs on, but only one computer in the whole thing. It's basically a case of us running around adjusting things."

This is more obvious in Jony Easterby's work Camera Vermicular, for he is sitting at a table, filming a bowl of snails (luxuriantly bedded on dahlias that the artist has been allowed to pluck from the gardens). "Oops, got to keep the performers from escaping," says Easterby, as a feisty little customer makes a bid for freedom. The image is projected split into four, such that watching the screen is like looking into a child's kaleidoscope, except that the picture occasionally resolves itself into identifiable antennae, shell or flesh.

"Look to the right, and you might see a meteor," says a cheery usher at the exit – which seems an appropriate coda to these spectacular man-made illuminations.

A garden of delights

The 37 acres of beautifully kept and scientifically significant gardens have become more and more attractive to festival-goers who value a haven from the relentless crowds of Princes Street and the Royal Mile.

• At Inverleith House, the small but perfectly formed gallery at the centre of the gardens, there is an exhibition of 14 rigorous minimalist sculptures (pictured) by American artist John McCracken. Apparently glossily mass-produced, the sheen of his primary-coloured blocks and slabs is actually painstakingly hand-created. Fascinating sketchbook drawings from the 1960s illuminate his process. Part of the Edinburgh international art festival.

•Susurrus is an audio guide with a difference. Audience members are given a map and an MP3 player, and then, according to the instructions they hear, wander through the gardens to a prescribed route, listening to an audio play by Scottish writer David Leddy. Susurrus has Britten's opera A Midsummer Night's Dream at its heart; as you stroll through the heathlands, the copses, and the rock garden, you could be one of Shakespeare's lost lovers. Part of Edinburgh festival fringe.